EVAL-AD5380EBZ Analog Devices Inc, EVAL-AD5380EBZ Datasheet - Page 21

• Manufacturer Part Number: EVAL-AD5380EBZ
• Description: Evaluation Board I.c.
• Manufacturer: Analog Devices Inc

Specifications of EVAL-AD5380EBZ

• Number Of Dac's: 40
• Number Of Bits: 14
• Outputs And Type: 40, Single Ended
• Sampling Rate (per Second): 125k
• Data Interface: DSP, I²C, MICROWIRE™, Parallel, QSPI™, SPI™
• Settling Time: 8µs
• Dac Type: Voltage
• Voltage Supply Source: Single
• Operating Temperature: -40°C ~ 85°C
• Utilized Ic / Part: AD5380
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

FUNCTIONAL DESCRIPTION
DAC ARCHITECTURE—GENERAL
The AD5380 is a complete, single-supply, 40-channel voltage
output DAC that offers 14-bit resolution. The part is available
in a 100-lead LQFP package and features both a parallel and a
serial interface. This product includes an internal, software
selectable, 1.25 V/2.5 V, 10 ppm/°C reference that can be used
to drive the buffered reference inputs; alternatively, an external
reference can be used to drive these inputs. Internal/external
reference selection is via the CR10 bit in the control register;
CR12 selects the reference magnitude if the internal reference
is rail-to-rail output capable of driving 5 kΩ in parallel with a
200 pF load.
The architecture of a single DAC channel consists of a 14-bit
resistor-string DAC followed by an output buffer amplifier
operating at a gain of 2. This resistor-string architecture guaran-
tees DAC monotonicity. The 14-bit binary digital code loaded
to the DAC register determines at what node on the string the
voltage is tapped off before being fed to the output amplifier.
Each channel on these devices contains independent offset and
gain control registers that allow the user to digitally trim offset
and gain. These registers give the user the ability to calibrate out
errors in the complete signal chain, including the DAC, using
the internal m and c registers, which hold the correction factors.
All channels are double buffered, allowing synchronous updat-
ing of all channels using the LDAC pin. Figure 27 shows a block
diagram of a single channel on the AD5380. The digital input
transfer function for each DAC can be represented as
where:
x2 is the data-word loaded to the resistor string DAC.
x1 is the 14-bit data-word written to the DAC input register.
m is the gain coefficient (default is 0x3FFE on the AD5380).
The gain coefficient is written to the 13 most significant bits
(DB13 to DB1) and the LSB (DB0) is zero.
n = DAC resolution (n = 14 for AD5380).
c is the14-bit offset coefficient (default is 0x2000).
INPUT DATA
x2 = [(m + 2)/ 2
×1 INPUT
m REG
c REG
REG
Figure 27. Single-Channel Architecture
×2
n
× x1] + (c – 2
DAC
REG
14-BIT
V
DAC
REF
n – 1
)
AVDD
R
R
VOUT
Rev. A | Page 21 of 40
The complete transfer function for these devices can be
represented as
x2 is the data-word loaded to the resistor string DAC. V
the internal reference voltage or the reference voltage externally
applied to the DAC REFOUT/REFIN pin. For specified
performance, an external reference voltage of 2.5 V is recom-
mended for the AD5380-5, and 1.25 V for the AD5380-3.
DATA DECODING
The AD5380 contains a 14-bit data bus, DB13 to DB0. Depend-
ing on the value of REG1 and REG0 (see Table 3), this data is
loaded into the addressed DAC input registers, offset (c)
registers, or gain (m) registers. The format data, offset (c), and
gain (m) register contents are shown in Table 12 to Table 14.
Table 11. Register Selection
REG1
1
1
0
0
Table 12. DAC Data Format (REG1 = 1, REG0 = 1)
11
11
10
10
01
00
00
Table 13. Offset Data Format (REG1 = 1, REG0 = 0)
11
11
10
10
01
00
00
Table 14. Gain Data Format (REG1 = 0, REG0 = 1)
11
10
01
00
00
VOUT = 2 × V
1111
1111
0000
0000
1111
0000
0000
1111
1111
0000
0000
1111
0000
0000
1111
1111
1111
1111
0000
DB13 to DB0
REG0
1
0
1
0
DB13 to DB0
DB13 to DB0
1111
1111
0000
0000
1111
0000
0000
1111
1111
0000
0000
1111
0000
0000
1111
1111
1111
1111
0000
REF
Register Selected
Input Data Register (x1)
Offset Register (c)
Gain Register (m)
Special Function Registers (SFRs)
× x2/2
1111
1110
0001
0000
1111
0001
0000
1111
1110
0001
0000
1111
0001
0000
n
1110
1110
1110
1110
0000
DAC Output (V)
2 V
2 V
2 V
2 V
2 V
2 V
0
REF
REF
REF
REF
REF
REF
Offset (LSB)
+8191
+8190
+1
0
–1
–8191
–8192
× (16383/16384)
× (16382/16384)
× (8193/16384)
× (8192/16384)
× (8191/16384)
× (1/16384)
Gain Factor
1
0.75
0.5
0.25
0
AD5380
REF
is